About 1 in 4 babies are now born to unmarried couples, a rate that has nearly doubled since 2002, according to a recent report from the Centers of Disease Control and Prevention (CDC).

The government has previously said that more than 40% of births are to unwed mothers, but the new report offers details showing that most such births occur in couples who aren’t married, but are living together.

“It’s thought that usually in births outside of marriage, one parent isn’t present. But many couples are cohabiting and these children do have two parents present,” says report author Gladys Martinez, a demographer in the CDC’s division of Vital Statistics.

The new data from the CDC’s National Center for Health Statistics was based on in-person interviews with more than 22,000 men and women aged 15 to 44 during 2006 through 2010, as part of the National Survey of Family Growth. The researchers then compared the data to a similar 2002 survey.

They found that 22% of births between 2006 and 2010 were to unmarried couples, up from 12% in 2002 and a threefold increase since 1985. About 23% of the reported births were to unmarried, cohabiting heterosexual couples, up from 14% in 2002. The CDC did not speculate on reasons for the increase.

“It’s such a large increase in such a short period of time,” says Martinez. “We cannot provide reasons for the increase, but overall, more couples are living together in general.”

Some argue that the recession may be responsible for the spike. “I think it’s economic shock,” Karen Benjamin Guzzo, a sociologist at Bowling Green State University in Ohio, toldUSA Today. “Marriage is an achievement that you enter into when you’re ready. But in the meantime, life happens. You form relationships. You have sex. You get pregnant. In a perfect world, they would prefer to be married, but where the economy is now, they’re not going to be able to get married, and they don’t want to wait to have kids.”

Although cohabiting parents may start out in very committed relationships, the researchers noted that the dynamic could still negatively influence kids over time. “One of the concerns with the increase in nonmarital childbearing is that children born outside of a marital union experience more family transitions, less stability and may have fewer resources,” the researchers said in the report.

“The challenge is kids with cohabiting parents are three times more likely to experience their parents’ break-up by the age of 5 than kids with married parents,” says Brad Wilcox, director of the National Marriage Project at the University of Virginia and associate professor of sociology. “They have less stability, security, legal and cultural support.”

As a consequence, Wilcox says kids in cohabiting homes are more likely to experience emotional problems, struggle in school and be more likely to use drugs later in life, compared with children of married parents. Based on his own research, kids in cohabiting homes do just as poorly in these areas as kids with single parents. “The fact is cohabiting relationships have remarkably lower levels of commitment. It gives the couple more flexibility, but less stability to the kids born into these relationships,” says Wilcox.

Education was a factor in the overall likelihood of pregnancy outside of marriage, according to the CDC. The survey found that 53% of women with a bachelor’s degree or higher had a biological child, compared with 88% with less than a high school diploma.

“These kids can be doubly disadvantaged because their parents are more likely to have less socioeconomic resources to support them,” says Wilcox.

But not everyone agrees that money is always an important predictor of a stable home life. “Having kids is much more than about money. It’s about love,” Guzzo told USA Today. “You can be a good parent if you don’t have a lot of money. You can be with someone who can be a good parent.”

The research team also found significant racial differences in the percentage of recent births outside of any sort of union — marriage or cohabitation. According to Martinez, in the last five years, such births were more common in black women than among Hispanics or whites. “We’ve seen racial difference across a lot of factors, but it was interesting to see the racial difference in terms of children outside of unions,” says Martinez. “The majority of recent births for black women occur out of any sort of union. That’s an increase.”

Additionally, the report found that more women who delay childbearing until after age 35 are having multiple kids. “As more women delay childbearing, we wonder whether or not they will be able to ‘catch up’ to the national average of two children,” says Martinez. “The percentage of older women having more than one child has greatly increased.” Since 1995, the percentage of late child-bearers has increased 75%.

The report was weighted to reflect the U.S. population and researchers hope the trends will support further research on reproductive and fertility experiences in men and women.